A switching system is provided in conventional telephone systems for interconnecting transmission paths between subscribers. In the contemporary systems employing PCM and TDM techniques, the switching systems are commonly based upon either a space-time-space configuration or upon a time-space-time configuration. U.S. Pat. No. 4,123,624 dated Oct. 31, 1978 by R. Gagnier et al and U.S. Pat. No. 3,851,105 dated Nov. 26, 1974 to A. Regnier et al depict examples of time-space-time switching systems.
In a time-space-time switching system, switching is accomplished by first switching a given channel in time, then switching it in space, and finally, once again switching it in time; hence the name time-space-time representing a time-switch, a space-switch, and a time-switch. In essence, a time-space-time switch functions to switch a channel from one assigned timeslot in an incoming bus to one assigned timeslot in an outgoing bus. This concept is well known in the art of switching. A space-time-space switch is similar in operation to the time-space-time switch except of course for the fact that it has two stages of space switching and only one stage of time switching.
Another concept to be considered in a switching system is network blocking. Network blocking refers to the inability of a switching system to provide a connection between two idle end-points. In other words, two subscribers cannot be connected together by the switching system because all available paths through the network (of the switching system) are in use. Present multistage switching networks (e.g. time-space-time switches) exhibit some degree of blocking. A single stage timeswitch is inherently non-blocking, but the number of channels that can be served a single timeswitch is limited by the speed of the memory devices employed. One object of the present invention is to provide a method and a circuit by which a relatively large (e.g. 2048 channels) non-blocking switching network may be constructed. Note, that for the purposes of this description, a switching network is considered to be comprised of a switching module (which performs the actual switching chores) and a control module to control the operation of the switching module.